In recent years, the composites industry has experienced a major shift from autoclave to out-of-autoclave (OoA) processing methods. This shift has been motivated by the high capital and operating costs of autoclaves as well as the long cycle times. As the demand for composites in commercial aircraft increases, autoclave processing will not be able to satisfy the required production rates. While there are advantages to OoA processing, a major disadvantage is the increased susceptibility to defect formation due to the absence of compaction pressure provided by an autoclave. Therefore, one major focus of the M. C. Gill Composites Center is defect reduction in composite parts made from OoA prepregs. The Composites Center has access to a wide variety of characterization, fabrication and processing techniques that enable comprehensive analysis of OoA prepregs. Our efforts have led to new insights into defect sources and mitigation strategies.
Sandwich structures, consisting of two (frequently composite) face sheets bonded on either side of a low-density core material, display excellent out-of-plane compression and shear properties with very low areal density. For this reason, composite sandwich structures have long appealed to the aerospace industry for use in weight-critical applications. Our research focuses on developing and using in situ process diagnostics and visualization to understand skin-core bond-line formation during cure. Experiments are coupled with physics-based process models to predict defects and guide process adjustments prevent them.
The composites industry presently sends most production scrap and EOL composites to landfills, and unsustainable practice that demands are technical solution. The M.C. Gill Composites Center, working with the Department of Chemistry, is developing approaches to chemical recycling the rely on oxidative catalysis under mild conditions. The aim is to recover both high-value components – fibers and matrix – and return to service in a sustainable manner.
Carbon fiber composites are increasingly used in high-temperature applications, driving the development of new resin systems such as benzoxazines and polyimides. These resins can be used to fabricate fan blades, ducts, or casings for jet and rocket engines, where service temperatures can reach several hundred degrees Celsius. Manufacturing techniques include compression molding and resin transfer molding (RTM). Due to the complex chemistry of these resins, the processing is significantly more challenging than for traditional epoxies. Research at the M.C. Gill Composites Center focuses on comprehensive materials characterization and the development of optimized manufacturing procedures. Through a combination of experiments and modeling, we demonstrate defect formation mechanisms and prevention strategies, and establish process windows and manufacturing guidelines as deliverables for our industrial sponsors.
Composite parts for aerospace are commonly produced by hand layup of prepregs and subsequent cure in autoclaves. The layup process is both labor-intensive and skill-intensive, incurring high costs. Working with USC’s Advanced Manufacturing Institute, we are developing methods to use robots to work in collaboration with humans to increase accuracy and reduce manufacturing costs.
Thermoplastic composites generally exhibit advantages that include high toughness, weldability, and long shelf-life. The Center is working to develop methods to produce high-toughness thermoplastic composites for NASA spacesuits. Efforts focus on developing novel approaches for combining fibers with thermoplastic matrix materials.
In aggressive service environments, metals generally fare better than composites, despite higher density and lower strength-to-weight ratios. USC’s Composites Center is exploring ways to use additive manufacturing to combine the durability of metallic alloys with the high specific strength of composites. The approach relies on the use of cold spray to deposit metallic layers onto composite parts, increasing resistance to erosion at high velocity.
Composite materials are used increasingly in high-temperature applications, such as jet engine components and hypersonic air vehicles. To meet the service requirements requires new materials and methods, such as ceramic matrix composites and carbon-carbon composites. The M.C. Gill Composites Center is collaborating with industrial partners to develop materials and manufacturing processes for both types of composites. In the CMC project, we are developing methods to rapidly densify ceramic powder-fiber blends by field-assisted sintering, reducing sintering times by more than 100X. In the C-C project, we are working with AMI to develop methods to automate the layup of prepreg plies.
Because the study of composite materials requires a cross-disciplinary perspective as well as a wide array of laboratory instrumentation, we recruit members from diverse backgrounds—including physics, chemical engineering, mechanical engineering, and, of course, materials science. This diversity in our infrastructure and the technical breadth of our staff puts us in the unique position to take on a broad range of projects sometimes only tangentially related to our primary areas of focus.